Why Use a Dehumidifier?

Why use a dehumidifier? It's a common question, one which is often posed as a challenge to anyone who recommends these appliances for the home.

There are two reasons for this sceptical attitude. People who recommend dehumidifiers have a habit of over-selling their benefits and dramatising the risks of excessive humidity. A dehumidifier is not the right answer for every case of excessive moisture but it can be the answer, or part of the answer, in many situations.

What we shall do in this article is to deal briefly with the main reasons why a dehumidifier may be used. We shall not deal with all the whys and wherefores, these are covered in a multitude of pages on this site. If any of the possible reasons relates to your needs you can research further, on this site and others, to decide whether a dehumidifier will be the right choice for you.

Personal Comfort

High relative humidity is uncomfortable for most people. We feel hot and sticky and it can seem like hard work to breathe. In high humidity conditions even opening windows gives no relief. If the air is very moist our sweat will not evaporate quickly and so we cool more slowly. The sweat remains on our skin in liquid form so we not only feel hot and sticky we are hot and sticky.

If we have air conditioning we can control the temperature. Running the air conditioning will also reduce relative humidity and, for many people, this is enough; so, why use a dehumidifier?

If the air conditioning is very effective it may reduce indoor temperature to the level set on the thermostat before relative humidity has been reduced to a comfortable level. Air conditioning responds to temperature, not to relative humidity. In this case a dehumidifier will help since it operates independently of the air conditioning. A portable model will make one area more comfortable, a whole house unit will provide comfort throughout the home.

An incidental benefit is that, because we feel cooler when there is less moisture in the air, it is now possible to set the thermostat a couple of degrees higher with no loss of comfort and an energy saving as a bonus.

If we don't have air conditioning we have two options; to use a dehumidifier or grin and bear it.

Personal Health

Where there is excessive moisture in the air mold will grow and dust mites will flourish. Neither of these two is pleasant to live with but the consequences of cohabiting with either may have an effect on our health. The greatest concern for most people is toxic black mold. The community of experts disagrees about how serious a health risk is presented by black mold, although all agree that there is some health risk.

We are neither qualified nor inclined to join that debate but assume that most people with any form of mold in the home will want to prevent further growth. The simple fact is that mold will flourish so long as relative humidity is too high. If we have tried every other means to reduce it, and failed, the answer to the question, why use a dehumidifier? is self evident.

Many people have existing health conditions that can be aggravated by mold and dust mites. Among these are respiratory disorders but by far the most common are allergies. Mold spores, and fecal matter produced by dust mites, are major causes of allergic reactions. The consequences are usually uncomfortable and sometimes more serious. Once again other means of humidity control may be appropriate but a dehumidifier will be effective. Why use a dehumidifier if one or more family members is allergic to mold spores and/or dust mites? Because the appliance, provided it is large enough for the area concerned, will reduce relative humidity quickly, usually within 48 hours.

Where is the most important place to use the unit to control mold and dust mite allergens? The crawl space or the basement; these are usually cooler than the rest of the home and have a higher relative humidity as a result. The allergens are drawn up through the rest of the house so can affect those who are sensitive to them even if the main living areas of the home are free from excessive humidity.

Condensation and Damp

Leaving aside the health issues, condensation, and the damp that may follow if it is not controlled, cause damage to the decor and contents of our homes. In extreme cases even the structure may be damaged. If damp does appear it is essential to eliminate any external source of water which may enter the home. This includes leaks in roofs and walls, blocked or damaged gutters and down spouts, poor drainage around the home and other sources of ground water ingress, particularly to crawl spaces and basements.

If the water is not coming from outside it must be coming from inside, from the air. If other remedies fail the answer to the question why use a dehumidifier? is why not? The potential cost of the damage far outweighs the price and energy cost of the appliance.

Sensitive Items

Many of us have items which are susceptible to damage if relative humidity is not controlled. One example is a piano.

Pianos are expensive and the more important music is to a person the more money she or he may spend on a high quality instrument. As all pianists know, the relative humidity around and inside a piano needs to be controlled to protect the instrument from damage. Recommendations about the precise upper and lower limits vary but there is near universal agreement that it is large fluctuations in relative humidity that are the cause of most serious damage.

A piano needs its own "micro climate" and humidity (and temperature) control are essential. Why use a dehumidifier? Because in most circumstances it is the only effective way of preventing the relative humidity within that micro climate from rising too far. A humidifier will often be required in addition, to prevent excessive dryness at other times of the year.

Another "special case" is the gun, more often guns, that many of us keep at home for recreation, protection and vermin control. Guns are usually kept in a gun safe or some other secure, enclosed space. There are many routines which experienced gun owners follow to protect their weapons and in many cases these may be sufficient. If, however, your gun safe is kept in a cool area, such as a basement, in an area where it is cold for some or all of the year, humidity control may be necessary to prevent corrosion.

As temperature falls relative humidity rises and if the dew point is reached condensation will occur. A means to absorb the water, such as a tub of silica gel, or a way of raising the temperature, a GoldenRod for example, may be a prudent precaution.


Boats and Recreational Vehicles (RVs) are often laid up for long periods and in colder climates can suffer from condensation inside. Many people find that ensuring some ventilation is sufficient to deal with this but this may be impractical or ineffective in some circumstances. Why use a dehumidifier? There is often no alternative as heating the boat/RV may be impossible or too expensive.

Full time RV'ers who experience cold winters will invariably suffer from condensation over night. RVs have a metal structure and react quickly to changes in ambient temperature, cooling inside much more rapidly than a house. With occupants producing water vapor through breathing, showering and cooking it is a constant problem to control humidity, particularly when it is too cold outside to allow proper ventilation. Many find a dehumidifier is the most effective solution although it has to be said the range of suitable models for such vehicles is limited and, in many cases, expensive.

It is to be hoped that manufacturers will respond to this need by producing more compact units, with a low centre of gravity (for stability when the vehicle is in motion) and genuine low temperature operating capability, all at affordable prices. At present Europe is rather better served by the range of models available than is the case in North America.


In brief, the answer to our question why use a dehumidifier? is; if all else fails, or is too expensive, use one. They do their job and, in many cases, what using one saves in financial and human cost far outweighs its purchase price and the energy dollars spent to run it.

Hopefully this brief discussion has begun to help you to find answer to the question, why use a dehumidifier?

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